Electric propulsion drive for watercraft

ABSTRACT

Devices and methods are disclosed related to electric propulsion drives for watercraft. In some embodiments, an electric drive includes an active cooling loop facilitated by a rotating electric motor pumping a coolant through a mast and a housing of the electric drive. The mast can be provided with a separation wall to separate and guide streams of cooler and hotter coolant. The motor and an ESC can be cooled by the coolant. In certain embodiments, the electric drive includes a rotor jacket that substantially surrounds an external rotor of an electric motor; the rotor jacket substantially reduces unwanted eddy currents, and thereby allows the use a large motor and a housing with a smaller external diameter, which reduces hydrodynamic drag. In one embodiment, the external rotor is coupled directly, without intermediary gearing, to a propeller.

RELATED APPLICATION

This application incorporates in its entirety, and hereby claims priority to, application 62/932,224 filed Nov. 7, 2020, titled ELECTRIC OUTBOARD FOR WATERCRAFT.

BACKGROUND 1. Technical Field

Embodiments of the invention disclosed generally relate to systems and methods for propulsion of watercraft using electric motor drives.

2. Description of the Related Art

The use of electric motors to provide propulsion for boats is known. Certain electric outboard motors operate at a voltage between 12 and 60 volts DC. Some outboard motors are powered with alternating current (AC). Conventional electric outboards generally use a motor assembly with a gear train and do not use liquid coolant to cool the motor and other internal components. These outboard motors require a relative large motor housing, and the gear trains usually produce frictional losses.

Some models require a large battery that is cumbersome to keep charged and stow. Certain designs employ an integral, rechargeable Lithium battery pack that can be removed for charging. Some designs of electric motors for watercraft propulsion are quiet, do not require refilling with inflammable gas, have no difficult pull-start or choke, no water pump and impellor, no gearbox or spark plugs (easy and cheap to maintain), and do not emit fumes. Power is also instant, and there is no requirement to warm them up before leaving the dock.

In terms of range, higher-quality lithium-powered models can run up to 3-4 hours at half-throttle with a range of around 10-12 miles. In calm, non-tidal waters this can even be extended to 15 miles in a small inflatable, if the throttle is managed properly for the objective.

United States Patent Application No. US20190344873A1 teaches an electric outboard with a motor below the water line. U.S. patent Ser. No. 10/745,095B2 teaches an electric outboard motor above the water line. U.S. patent Ser. No. 10/358,202B2 teaches an electric outboard motor that uses a planetary gear train.

There is a need in the art to reduce hydrodynamic drag without causing eddy currents. There is a need in the art to provide designs with relatively larger motors to, among other things, enable direct drive and reduce the outside diameter of the motor housing.

SUMMARY OF ILLUSTRATIVE EMBODIMENTS

Disclosed are systems and methods for propulsion of watercraft. One aspect of the invention is directed to a propulsion drive having a housing; a mast coupled to the housing; wherein the housing is configured to be in fluid communication with the mast to allow inflow of cooled coolant from the housing into the mast and outflow of heated coolant from the mast back into the housing; a separation wall within the mast, the separation wall configured to provide a separation between the cooled coolant and the heated coolant; and a motor located within the housing, the motor configured whereby a rotation of the motor causes the coolant to flow in a cooling loop from the housing into the mast and from the mast back into the housing.

In one embodiment, the propulsion drive includes an ESC, wherein the ESC is located in the mast. The ESC can be located at a distal end of the mast away from the housing. In some embodiments, the motor and the ESC are configured to be submerged in the coolant. In another embodiment, the motor is an external rotor electric motor. In yet other embodiments, the electric drive includes a rotor jacket substantially enclosing the motor.

Another aspect of the invention concerns a propulsion drive having a housing; a motor located within the housing, the motor comprising an external rotor; a rotor jacket substantially surrounding the external rotor; and wherein the rotor jacket is configured to reduce an eddy current generated by the motor. In some embodiments, the electric drive includes a propeller shaft coupled to the motor and to a propeller, wherein the motor is coupled to the propeller directly via the shaft without intermediary gearing. In yet another embodiment, the rotor jacket comprises surface textures and/or structures to facilitate the pumping of a coolant in and out of the housing. In other embodiment, the electric drive includes a mast configured to be in fluid communication with the housing. In one embodiment, the mast has a separation wall configured to create a cooled coolant passage and a heated coolant passage within the mast.

Yet another aspect of the invention relates to a method of cooling a propulsion drive having a motor and an ESC. The method includes the steps of providing a mast; providing a separation wall within the mast to create a first compartment and a second compartment, wherein the first compartment is configured to facilitate inflow of cooled coolant, and wherein the second compartment is configured to facilitate outflow of heated coolant; providing a housing configured for fluid communication with the mast, wherein the housing and mast are configured to facilitate a flow of the coolant in a cooling loop from the housing into the mast and back into the housing; and submerging the motor and the ESC in the coolant by filling the mast and the housing with the coolant. In one embodiment, the method includes pumping the coolant through the cooling loop via a rotation of the motor.

In another aspect of the invention, it involves a method of manufacturing an outboard electric motor. The method of manufacture includes the steps of providing an external rotor electric motor; providing a rotor jacket that substantially encloses the external rotor electric motor; and providing a housing sized and shaped to geometric tolerances around the rotor jacket to minimize an outside diameter of the housing. In one embodiment, the method further includes providing a hollow mast configured to be in fluid communication with the housing. In another embodiment, the method includes providing a separation wall within the mast to provide a first compartment for a cooled coolant and a second compartment for a heated coolant. In certain embodiments the method includes providing an ESC within the hollow mast. In one embodiment, the method includes providing a propeller and a propeller shaft, and directly coupling the external rotor electric motor to the propeller via the propeller shaft. In yet other embodiments, the method further includes providing a sight glass indicator on the hollow mast. In one embodiment, the method involves providing an ESC external to the hollow mast and configured to be in thermal communication with the hollow mast whereby a flow of coolant within the mast cools the ESC.

The above as well as additional features and advantages of the present invention will become apparent in the following detailed written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is schematic, cross-sectional view of one embodiment of an inventive propulsion drive.

FIG. 2 is a perspective view of one application of the propulsion drive of FIG. 1.

FIG. 3 is a detail, cross-sectional view of a motor and a rotor jacket used with the propulsion drive of FIG. 1.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description of exemplary embodiments of the invention, specific exemplary embodiments in which the invention may be practiced are described in sufficient detail to enable those skilled in the relevant technology to practice the invention, and it is to be understood that other embodiments may be used and that mechanical, electrical and other changes may be made without departing from the spirit or scope of the present invention.

Known electric outboards use a dry motor pod assembly with gear train. This requires a large motor pod housing and the gear train develops frictional losses. Inventive embodiments of the invention disclosed address this problem.

Disclosed embodiments of an electric outboard use a direct drive system within a tight fitting housing, which is enabled by the use of an eddy current reduction jacket. The jacket allows use of a larger torque motor, which then allows both use of direct drive of the propeller shaft and reduction of the outside diameter of the motor pod housing.

In one embodiment, the electric outboard is filled with oil to dissipate heat generated by the motor and the ESC. The oil is actively pumped by the rotating rotor of the motor.

In one embodiment, the efficiency losses of the gear train are eliminated. The part count of the system is reduced thereby increasing efficiency and reducing maintenance. Water leaks into the motor housing are eliminated and the internal electronics are cooled through the use of the active oil cooling.

Large cross-sectional profile leads to more hydrodynamic drag. More moving parts lead to more frictional losses.

In one embodiment, the cross-sectional area is reduced by adding a low carbon steel jacket to the motor, which allows tighter fitment inside the motor pod without causing eddy currents. This also allows use of a larger motor allowing direct drive and reducing the outside diameter of the motor pod.

One embodiment includes (1) a direct drive external rotor brushless motor, (2) a motor pod/housing, (3) a cooling oil, (4) an eddy current reduction jacket, (5) an oil divider wall, and an (6) ESC.

Motor 1 is covered by jacket 4 to reduce eddy currents and allow tighter fit inside housing 2. This also reduces the overall diameter of housing 2. Motor 1 pumps oil 3 by the rotating action up through the housing 2 and around wall 5 which allows oil 3 to reach the ESC 6 thereby cooling critical components. Oil 3 actively circulates up and down within housing 2 while motor 1 rotates. Seawater around housing 2 cools oil 3 before it cycles back up housing 2.

In one embodiment, an eddy current reduction jacket on the external rotor brushless motor reduces the gap between the internal diameter of the housing and the external diameter of the rotor. This allows to fit a larger motor in the housing, which then allows eliminating the use of a planetary gear train after the motor. The active cooling oil circulation allows placement of the ESC away from the motor at the top of the mast housing assembly. This design allows advantageous use, in some embodiments, of off the shelf ESC and motor instead of custom electronics.

One embodiment includes a housing, ESC, oil divider wall, prop shaft, and other basic elements of an electric outboard, like tiller and transom bracket. The housing is made of extruded aluminum shapes which are cut and welded together. Mounts for the motor are made from CNC aluminum parts and these are attached to the welded assembly with fasteners. These bushings hold the motor and propeller shaft/bearings in proper position. The oil divider wall is placed in the top of the welded assembly along with the ESC unit which is wired to the motor in the bottom of the housing. A low carbon steel sheet (eddy current reduction jacket) is added to outside of the rotor before installation in the housing. Then seals are pressed in to prevent egress of fluid from the propeller shaft. Oil is then poured into the top of the housing (mast) until the ESC is submerged. Then the other basic subassemblies are added like top housing cover, tiller and transom bracket.

In certain embodiments, the elements are external rotor brushless motor, cooling oil, ESC, motor housing, propeller shaft, seals, housing cover, bearings, mounting bushings, and propeller. Optional elements include anti cavitation plate and tiller.

In one embodiment, the ESC can be placed in the dry area outside the housing as long as it's still coupled to the cooling oil through a heat sink. All of the CNC machined parts can be made of molded metals and geometries can be adjusted to suit. The transom bracket can also be molded.

The drive can be attached to a watercraft and used to propel the watercraft in a more efficient manner. Some applications include sail pods, submarines, inboards, embedded in rudder.

Referencing FIG. 1, in one embodiment an electric drive 100 includes a mast 102 coupled to a housing 104. Mast 102 and housing 104 are in fluid communication. Housing 104 includes a nose cone 106. Housing 104 and nose cone 106 are in fluid communication.

Electric drive 100 includes an electric motor 112. Motor 112 has a stator (not shown separately) and an external rotor (not shown separately). The stator is rigidly coupled to housing 104. The rotor is coupled directly to a propeller 108 via a propeller shaft 110. Hence, in one embodiment, drive 100 does not use the typical gear train used in these types of drives. Motor 112 can be, for example, an external rotor, brushless electrical motor. In some embodiments, drive 100 includes a rotor jacket 114 that substantially encloses motor 112.

Mast 102 includes a coolant inlet 116 and a coolant outlet 122. Mast 102 further includes a separation wall 118. Each of coolant inlet 116 and coolant outlet 122 is in fluid communication with a corresponding coolant outlet and coolant inlet in housing 104. In some embodiments an electronic speed control (ESC) 124 is included in mast 102 and placed at a distal end of mast 102 away from housing 104. In one embodiment, mast 102 includes a sight glass 134 incorporated into the body of mast 102.

Mast 102 can be made, for example, through well-known aluminum extrusion processes. The separation wall 118 provides a first compartment for allowing the passage of cooler coolant 128 up through mast 102, and into a second compartment that returns a hotter coolant 130 back into housing 104 via coolant outlet 122. In one embodiment, the coolant can be oil. In some embodiments, a very low viscosity oil is preferred; one such oil can be, for example, PSF-1 cSt Pure Silicone Fluid Octamethyltrisiloxane, which is manufactured by Clearco Products Co. of Pennsylvania.

FIG. 2 shows a perspective view of an application of one embodiment of electric drive 100. In one embodiment, electric drive 100 includes a mast cap 120 coupled to mast 102. A tiller 126 can be coupled to mast cap 120. The use of tillers such as tiller 126 is well-known in the art. Electric drive 100 can be further provided with a transom bracket 132 for attaching electric drive 100 to a watercraft. In some embodiments, mast 102 is coupled to an anti-cavitation plate 136.

FIG. 3 shows a perspective, cross-section of a detail of electric drive 100 shown in FIG. 1. In one embodiment, electric drive 100 includes motor 112 that is substantially surrounded on its lateral sides by rotor jacket 114. In certain embodiments, motor 112 is an external rotor motor; hence, rotor jacket 114 substantially surrounds the external rotor of motor 112. Advantageously, use of rotor jacket 114 reduces undesired magnetic flux produced by motor 112; thereby allowing the use of larger motors and smaller housings for certain applications of providing propulsion to watercraft.

During operation, in one embodiment, the rotation of motor 112 acts as a pump to drive coolant through housing 104, including nose cone 106, into mast 102. Coolant is cooled by, for example, housing 104 and nose cone 106 being in contact with seawater, and the seawater carrying away the heat produced by drive 100. Cooled or cooler coolant 128 is pumped into coolant inlet 116 by the rotating action of motor 112. Cooled coolant 128 flows on one side of separation wall 118, submerges ESC 124, thereby cooling ESC 124, and flows into the other side of separation wall 118. Hotter or heated coolant 130 then flows on one side of separation wall 118 into housing 104 through a coolant inlet of housing 104. In one embodiment, the location of ESC 124 in mast 102 advantageously facilitates use an off-the-shelf ESC, rather than being limited to using custom electronics. In some embodiments, rotor jacket 114 is provided with structural and/or textural elements (for example, grooves, channels, ridges, and the like) to promote the pumping of the coolant. In one embodiment, rotor jacket 114 is made of a low carbon steel; preferably less than 0.3% carbon steel. In some embodiments, the thickness of rotor jacket 114 is selected to appropriately reduce stray magnetic flux below a selected operational level. In some embodiments, the thickness of rotor jacket 114 is selected based on appropriate geometric tolerances for manufacture and operation of fit of rotor jacket 114 inside housing 104. In one embodiment a motor 112 has an external rotor 112B with a 3-inch external diameter; the thickness of rotor jacket 114 is preferably about 35-thousandths (0.035) of an inch; and the gap between rotor jacket 114 and an internal diameter of housing 104 is 50-thousandths (0.050) of an inch. In certain embodiments, the thickness of rotor jacket 114 is from about 0.025-inch to about 0.075-inch in thickness.

In one embodiment, rotor jacket 114 can be used to reduce eddy currents produced by an external rotor of motor 112. Use of rotor jacket 114 reduces the gap between an internal diameter of housing 104 and an external diameter of the rotor of motor 112. Advantageously, it is then possible to fit a relative larger motor 112 in housing 104 when compared to other drives designs for the same purpose of marine propulsion.

Another advantage, as a result of the use of a larger motor 112, is that drive 100 in some embodiments can be configured such that propeller 108 is driven directly by motor 112, through shaft 110, without an intervening gear train.

In one embodiment, mast 102 is filled with coolant until the coolant level is visible through sight glass 134. Advantageously, the height of the coolant in mast 102 ensures that the pressure inside mast 102 is always higher than atmospheric pressure. Hence, if drive 100 were to leak (for example, coolant loss through a seal of shaft 110 or of nose cone 106), the coolant level would drop until reaching equilibrium. This equilibrium prevents seawater from entering drive 100 system and damaging electronics, such as ESC 124. The coolant level drop can be viewed through sight glass 134, or coolant level drop can be detected by an auxiliary coolant level sensor, which can sound an alarm and/or shut down drive 100.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the relevant technology that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular system, device or component thereof to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed for carrying out this invention. 

What is claimed is:
 1. A propulsion drive comprising: a housing; a mast coupled to the housing; wherein the housing is configured to be in fluid communication with the mast to allow inflow of cooled coolant from the housing into the mast and outflow of heated coolant from the mast back into the housing; a separation wall within the mast, the separation wall configured to provide a separation between the cooled coolant and the heated coolant; and a motor located within the housing, the motor configured whereby a rotation of the motor causes the coolant to flow in a cooling loop from the housing into the mast and from the mast back into the housing.
 2. The propulsion drive of claim 1, further comprising an ESC, wherein the ESC is located in the mast.
 3. The propulsion drive of claim 2, wherein the ESC is located at a distal end of the mast away from the housing.
 4. The propulsion drive of claim 2, wherein the motor and the ESC are configured to be submerged in the coolant.
 5. The propulsion drive of claim 1, wherein the motor is an external rotor electric motor.
 6. The propulsion drive of claim 1, further comprising a rotor jacket substantially enclosing the motor.
 7. A propulsion drive comprising: a housing; a motor located within the housing, the motor comprising an external rotor; a rotor jacket substantially surrounding the external rotor; and wherein the rotor jacket is configured to reduce an eddy current generated by the motor.
 8. The propulsion drive of claim 7, further comprising a propeller shaft coupled to the motor and to a propeller, wherein the motor is coupled to the propeller directly via the shaft without intermediary gearing.
 9. The propulsion drive of claim 7, wherein the rotor jacket comprises surface textures and/or structures to facilitate the pumping of a coolant in and out of the housing.
 10. The propulsion drive of claim 6, further comprising a mast configured to be in fluid communication with the housing.
 11. The propulsion drive of claim 10, wherein the mast comprises a separation wall configured to create a cooled coolant passage and a heated coolant passage within the mast.
 12. A method of manufacturing an outboard electric motor, the method comprising: providing an external rotor electric motor; providing a rotor jacket that substantially encloses the external rotor electric motor; and providing a housing sized and shaped to geometric tolerances around the rotor jacket to minimize an outside diameter of the housing.
 13. The method of claim 12, further comprising providing a hollow mast configured to be in fluid communication with the housing.
 14. The method of claim 13, wherein providing a hollow mast further comprises providing a separation wall within the mast to provide a first compartment for a cooled coolant and a second compartment for a heated coolant.
 15. The method of claim 14, further comprising providing an ESC within the hollow mast.
 16. The method of claim 12, further comprising providing a propeller and a propeller shaft, and directly coupling the external rotor electric motor to the propeller via the propeller shaft.
 17. The method of claim 13, wherein providing a hollow mast further comprises providing a sight glass indicator on the hollow mast.
 18. The method of claim 13, further comprising providing an ESC external to the hollow mast and configured to be in thermal communication with the hollow mast whereby a flow of coolant within the mast cools the ESC. 